Rap1p, an essential DNA binding protein of Saccharomyces cerevisiae plays roles in silencing large stretches of Chromatin and in the activation and repression of hundreds of genes. In rapidly growing yeast cells, many of the genes regulated by Rap1p are among the most highly transcribed in the genome; however, during other growth conditions, including meiosis, many of the same genes are repressed. Understanding how a single transcription factor can mediate different transcriptional responses based on cell type, stage of development or growth conditions is a fundamental biological problem. The experiments described in this proposal are designed to identify factors that allow Rap1p to evoke different transcriptional outcomes during meiosis as compared to vegetatively growing cells. First, the distribution of Rap1 p and its affects on patterns of expression in vegetative growth and throughout meiosis will be mapped using ChlP-chip and expression microarray experiments. We will then compare the patterns of distribution under each condition and correlate binding patterns with gene expression. Finally, using sensitive reporter assay systems, we will perform screens to identify and characterize cofactors, competing transcription factors and protein modifiers that are required for modulating the activity of Rap1p during meiosis.